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The HK417 is similar in internal design to the HK416, although the receiver and working parts are enlarged to suit the larger 7.62×51mm cartridge. The bolt is a seven-lug rotating type, which sits in a bolt carrier and operates in a forged alloy receiver resembling those of the Stoner-designed AR-10, AR-15 and M16 rifles.

The early HK417 prototype used 20-round magazines from the Heckler & Koch G3 rifle family, which did not feature a bolt hold-open device. Later prototypes, however, switched to a polymer magazine with bolt hold-open. The magazine resembles an enlarged version of the G36's transparent magazine, except without the pins for holding more than one magazine together.

Purchasers of the HK417 have typically intended it to complement lighter assault rifles chambered for less powerful intermediate cartridges (often 5.56×45mm NATO), for the designated marksman role. The HK417's greater accuracy, effective range, and penetration offset its greater expense, its lower rate of fire, and its smaller ammunition capacity both in magazine and carriage.[3]

The HK417 A2 is the improved version. The design of the receiver, barrel interface, gas port and the bore axis alignment of the rifle have been further optimised to increase its accuracy and reliability.[1][3] The German Army uses the HK417 A2 - 13″ with the designation G27.[3][4]

As of 2013, the HK417 A2 models chambered for 7.62×51mm NATO available to the military and law enforcement market are:

HK417 A2 - 13″: carbine with 330.2 mm (13 in) barrel

HK417 A2 - 16.5″: rifle with 419.1 mm (16.5 in) barrel

HK417 A2 - 20″: "full size" rifle with 508.0 mm (20 in) barrel

Accurized barrels provide 0.3 mil (1 moa) accuracy (with match grade ammunition). A barrel can be changed in under two minutes with simple tools. All HK417 barrels are cold hammer forged and chrome-lined and use a conventional lands and grooves bore profile with a twist rate of 1 turn in 279.4 mm (11.00 in). They are designed to function reliably with bullet weights ranging from 9.3 to 11.34 g (144 to 175 gr) and are threaded for a flash hider or sound suppressor.[3][5]

The civilian MR308 was used to develop the G28, a designated marksman rifle for the German Bundeswehr (Federal Army) deployment to the War in Afghanistan. The semi-automatic G28 is chambered for 7.62×51mm NATO and has a factory warrantied accuracy of 45 mm dispersion at 100 meters (0.45 mil or 1.5 moa) when fired with 10 rounds using OTM/HPBT/Sierra Match King ammunition. The G28 features STANAG 4694 NATO Accessory Rails that are backwards-compatible with the STANAG 2324/MIL-STD-1913 Picatinny rails. The upper receiver is made from steel instead of HK's aluminium alloy. Approximately 75% of the parts are interchangeable with the HK417. There are two different versions of the G28: G28 E2 (Standard) with a Schmidt & Bender 3–20×50 PM II (modified to Bundeswehr requirements) and the G28 E3 (Patrol) with Schmidt & Bender 1–8×24 PM II.[6] By October 2017, Heckler & Koch had renamed the G28 as the HK241, though G28 remains its Bundeswehr designation.[7]

In March 2018, the Army announced that a version of the G28/M110A1 would be issued to infantry squads as the service's standard Squad Designated Marksman Rifle (SDMR). Issuing a 7.62 mm SDMR is meant to increase individual squads' ability to defeat enemy body armor that standard 5.56 mm rounds cannot penetrate.[12] The M110A1-based rifle will replace the M14 EBR, in use by the Army since 2009, but because it was based on an operational needs statement it had to be turned in by units at the end of a combat deployment. Unlike the sniper configuration, the marksman version is fitted with a simpler rifle optic instead of a telescopic sight to make quick adjustments between 0-600 meters, and it fires M80A1 Enhanced Performance Rounds rather than sniper rounds; it will be fielded with a suppressor to make the marksman less identifiable with louder 7.62 mm rounds. Roughly 6,000 are planned to be fielded with one per squad in infantry, engineer and scout formations starting in late 2018.[13]

The MR308 is a civilian variant of the HK417, introduced in 2007 alongside the MR223, a civilian HK416.[14] It is a semi-automatic rifle with several "sporterized" features. At the 2009 SHOT Show, the two rifles were introduced to the American civilian market as the MR762 and MR556, respectively.[15] Since then both were replaced by the improved MR762A1 and MR556A1.[16][17]